1. Field of the Invention
The present invention relates generally to an air-conditioner for automobiles, and more particularly to an improvement in a control system for controlling the displacement of a compressor provided in a refrigeration cycle or system of the automobile air-conditioner.
2. Description of the Prior Art
There are known automatically controlled automobile air-conditioners of the type wherein the displacement of a compressor is controlled by a thermal load on the vehicle compartment which is calculated in the form of a total signal based on a setting temperature, a vehicle compartment temperature, and a temperature outside the vehicle compartment. The prior automobile air-conditioners have a drawback that the temperature of air passed through an evaporator cannot be maintained at a constant value due to a change in temperature of intake air or a change in amount of air supplied from a blower. Consequently, an accurate control of the vehicle compartment temperature is difficult to achieve.
With the foregoing drawback in view, an attempt has been proposed such as disclosed in Japanese Pat. Laid-open Publication No. 62-94748, for example, wherein the degree to which the evaporator is cooled is detected and the thus detected degree of cooling of the evaporator is used in combination with the total signal stated above for correcting the displacement of the compressor.
This correction of the displacement of the compressor is effected after detection of a change in the degree of cooling of the evaporator and not in coincidence with a change in temperature of intake air or a change in amount of air supplied from the blower based on which the degree of cooling of the evaporator varies. Consequently, an unpleasant temperature change is produced due to a delay in correction of the displacement of the compressor. Thus, the prior control system only has a limited accuracy in controlling the temperature of air discharged into the vehicle compartment.